The invention relates to a process for the preparation of organosilicon compounds.
It is known that silylalkylpolysulphanes can be prepared substantially by a nucleophilic substitution on chloroalkylsilanes with anionic polysulphides prepared in various ways (German Patent DE-PS 2141159). The working-up of the mixture consisting of the organosilicon compounds and of the solid formed in the nucleophilic substitution, in the present case a salt, is effected by filtration or centrifuging. The resulting salt is very finely divided if it is precipitated from an organic phase.
Furthermore, U.S. Pat. No. 6,777,569 discloses a process for the preparation of blocked mercaptosilanes, the metal salt of an organosilicon compound containing a mercapto group being reacted with an acyl halide in the presence of toluene. The working-up of the mixture consisting of the organosilicon compound and of the salt formed in the nucleophilic substitution is effected by complete dissolution of the salt in demineralized water and subsequent phase separation. The phase separation is decisively supported by the presence of toluene. In addition to the organosilicon compound, the organic phase therefore contains toluene, which has to be removed by distillation after the phase separation.
U.S. Pat. Nos. 5,405,985, 5,468,893, 5,663,396, 5,583,245 and EP-A 0694552 disclose processes which prepare the corresponding polysulphide in aqueous solution from sulphides and sulphur and react them in a two-phase system with haloalkylsilanes in the presence of toluene and a phase-transfer catalyst to give polysulphanes. In this procedure, the working-up of the mixture consisting of the organosilicon compound and of the salt formed in the nucleophilic substitution is effected by complete dissolution of the salt in demineralized water and subsequent phase separation. The phase separation is decisively supported by the presence of toluene. In addition to the organosilicon compound, the organic phase therefore contains toluene, which has to be removed by distillation after the phase separation. In this procedure, the phase-transfer catalyst or its degradation product remains in the sulphur-containing organosilicon compounds with a so far unexplained influence on the performance characteristics of the bis(silylalkyl)polysulphanes.
Furthermore, U.S. Pat. Nos. 6,448,426, 6,384,255, 6,384,256, WO 03/002573, WO 03/002576, WO 03/002577, WO 03/002578 and WO 04/043969 disclose processes which prepare the corresponding polysulphide in aqueous solution from sulphides and sulphur or hydrogen sulphides, alkali metal hydroxides and sulphur and react them in a two-phase system with haloalkylsilanes in the presence of a phase-transfer catalyst to give polysulphanes. The working-up of the mixture consisting of the organosilicon compound and of the salt formed in the nucleophilic substitution is effected by complete dissolution of the salt in water and subsequent phase separation. In this procedure, the phase-transfer catalyst or its degradation products remain in the sulphur-containing organosilicon compounds with a so far unexplained influence on the performance characteristics of the bis(silylalkyl)polysulphanes.
A disadvantage of the known processes in which the organosilicon compounds are prepared under anhydrous conditions is the difficult and expensive removal of the finely divided solids forming.
It is an object of the invention to provide a process which makes it possible to work up mixtures consisting of organosilicon compounds and solids in a manner which is as simple and economical as possible.
A further disadvantage of the known processes in which the polysulphanes are obtained by reacting the corresponding polysulphide, which is obtained in aqueous solution from sulphides and sulphur, in a two-phase system with haloalkylsilanes in the presence of a solvent, such as, for example, toluene, is that the sulphur-containing organosilicon compounds have to be freed from the solvent, for example by vacuum distillation. Another disadvantage is that the solvent obtained optionally has to be dried before further use.
A further object of the invention is to provide a process that permits the preparation of sulphur-containing organosilicon compounds which require no solvent for supporting the phase separation.
A further disadvantage of the known processes in which the polysulphanes are obtained by reacting the corresponding polysulphide, which is obtained in aqueous solution from sulphides and sulphur, in a two-phase system with haloalkylsilanes in the presence of a phase-transfer catalyst is that the sulphur-containing organosilicon compounds are contaminated with the phase-transfer catalyst or its degradation products.
A further object of the invention is to provide a process that permits the preparation of sulphur-containing organosilicon compounds which are free from a phase-transfer catalyst essential to the process or its degradation products.